On your website/label you advice to use PK 13/14 one week while a shop recommended me to use it more weeks?

We recommend to use PK 13/14 always for one week! CANNA feeding already contains a certain amount of P and K. When the plant is in a certain stage of the flowering stage we can't increase the feed for the plant any more, so we change the PK-ratio by adding PK 13/14 for one week.

Soak rock wool before use

Never use raw rockwool! The pH is too high. Always soak rockwool before using it for the 1st time. Soak with water or a nutrient mixture with the pH adjusted to 5 and an EC of about 1.3 (ppm values). CANNA Start has been specially developed for this purpose. As well as correcting pH & EC, a pre-soak also ensures an even distribution of the nutrient solution throughout the slab.